Can I Pass a Table as a Parameter to a SQL Server Scalar UDF?

Passing Tables as Parameters to SQL Server UDFs

Is it possible to pass a table as a parameter into a scaler UDF?

Yes, it is possible to pass tables as parameters into scaler UDFs. However, not all table types are supported.

Restrictions on Table Types

According to Microsoft's documentation, all data types, including CLR user-defined types and user-defined table types, can be used as parameters except for the timestamp data type.

User-Defined Table Types

To pass a table as a parameter, you need to create a user-defined table type. For example:

CREATE TYPE TableType AS TABLE (LocationName VARCHAR(50))

Example UDF

The following UDF takes a user-defined table type as a parameter:

CREATE FUNCTION Example( @TableName TableType READONLY)
RETURNS VARCHAR(50)
AS
BEGIN
    DECLARE @name VARCHAR(50)

    SELECT TOP 1 @name = LocationName FROM @TableName
    RETURN @name
END

Note that the parameter must be specified as READONLY.

Example Usage

To use the UDF, declare a variable of the user-defined table type and insert data into it:

DECLARE @myTable TableType
INSERT INTO @myTable(LocationName) VALUES('aaa')

You can then call the UDF:

SELECT dbo.Example(@myTable)

Using Data from a Table

If you have data in a table that you want to pass to the UDF, you can use a variable to store the data:

DECLARE @myTable TableType
INSERT INTO @myTable(field_name)
SELECT field_name_2 FROM my_other_table

You can then pass the variable to the UDF:

SELECT dbo.Example(@myTable)

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